Journal of Reliable Power - SEL

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10 Fig. 18 illustrates some of the these considerations. Short lines present sufficient margin to accommodate the inner and outer zones together with any type of distance element, such as a quadrilateral distance unit, following the above guidelines. Long transmission lines, however, may not allow sufficient margin. Engineering judgment should be used to set the inner and outer zones, as well as the resistive reach of the quadrilateral element. When determining the setting parameters, it may be very difficult to cover all possible scenarios of instability with a simple two-source model. Therefore, transient studies will be needed to understand the effectiveness of the scheme in Fig. 18. Recently, a power swing detection algorithm was proposed that requires little information from the user [18]. This algorithm will detect and declare a power swing based on the estimation of the swing center voltage (SCV), which is the voltage at the electrical center of a two-source model. This voltage can be estimated with local measurements and its behavior used to detect an out-of-step condition. The advantage of this methodology is that no network information is required. D. Series Capacitor Applications It is common to apply directional comparison relaying systems in the protection of series-compensated transmission lines. Protective relays intended to protect these lines should be designed to accommodate the changing measured impedance (because of the MOVs [metal oxide varistors] and spark gaps in parallel with the capacitor bank) and subsynchronous voltages and currents that are characteristic of series capacitor-compensated systems [19]. Moreover, protective relaying systems located in adjacent lines should reliably determine the direction to a fault. For distance elements that are polarized with voltage, like mho distance elements, the voltage inversion because of the series capacitor is properly handled with memory voltage [19][20]. Moreover, directional elements determine the correct direction to the fault [21]. Identifying the fault direction is important to keep the reactance and resistance lines of the quadrilateral distance element from operating improperly. An impedance-based negative-sequence polarized directional element (or an alternate zero-sequence polarized element for ground faults) will properly determine the direction to the fault, unless a current inversion is present. Depending on the location of the capacitor bank and the location of the voltage transformers (VTs), suggested settings for the directional thresholds (Z2F and Z2R) can be found in [20] and [21]. For the impedances of the compensated system in Fig. 19, the directional element threshold Z2F should be set to: (ZL1 − XC) Z2F ≤ (17) 2 Setting this threshold as close to the origin as possible will ensure proper directional determination, unless a current reversal is possible in the power system. jX –jXC ZL1 Fig. 19. Series capacitor applications Uncompensated Compensated In Fig. 19, the perspective of a long line is shown. Seriescompensated lines are long lines that require compensation to transfer more power. There are no short lines compensated with series capacitors. Also, in the vicinity of a series capacitor installation, subsynchronous oscillations of the voltages and currents are possible [19][20][21]. While the filtering in protective relays is very good at eliminating highfrequency components, the filtering is not efficient at eliminating lower frequencies. These subsynchronous transients, shown as impedance oscillations on the apparent impedance plane, eventually converge on the true apparent impedance, as illustrated in Fig. 20. This figure also shows that distance element overreach is a possibility. jX Z1L –jXc Fig. 20. Subharmonic frequency transients can cause distance elements to overreach R R 74 | Journal of Reliable Power
11 Zone 1 distance elements should account for the above phenomena by reducing the reach [20][21]. A good suggestion is to set the reach of the reactive line to half of the compensated line impedance [20]. On the other hand, protective relays can have an automatic reach adjustment based on a measured apparent impedance compared to a theoretically calculated value [14][21]. This way, the reach is automatically reduced to half of the compensated line impedance when transients are detected. The resistive reach should follow the recommendations for a long line (e.g., Rset equal to one-half Zset). The presence of the series capacitor in the power system modifies the homogeneity of the negative- and zero-sequence impedances. Therefore, when adjusting the homogeneity factor T, described in (18) and (19), the capacitor impedance should be considered. When using a negative-sequence current polarized reactance element: ⎛ IF2 ⎞ ⎡ ZS1 + ZL1 − XC + ZR1 ⎤ T = arg⎜ ⎟ = arg IR2 ⎢ ZR1 + (1 − m)(ZL1 − XC) ⎥ (18) ⎝ ⎠ ⎣ ⎦ And when using a zero-sequence polarized reactance line: ⎛ IF0 ⎞ ⎡ ZS0 + ZL0 − XC + ZR0 ⎤ T = arg ⎜ ⎟ = arg IR0 ⎢ ZR0 + (1 − m)(ZL0 − XC) ⎥ (19) ⎝ ⎠ ⎣ ⎦ Notice that the zero- and negative-sequence impedance of a series capacitor are the same as the positive-sequence impedance. Equation (18) for the uncompensated line should also be evaluated. The minimum calculated T value (most negative) should be used. When applying any protective relaying scheme to seriescompensated lines, transient simulation and testing are recommended [19][21]. This step ensures dependability and confirms proposed settings. E. Single-Pole Trip Applications In transmission line protection, it is common to use singlepole trip schemes. The scheme trips the faulted phase only for a single-line-to-ground fault. Once the pole is open, the other two phases are still conducting power, and the system is capable of remaining synchronized. During the open-pole interval, it is expected that the arc deionizes. After the openpole interval, a reclosing command is sent to the breaker. Current polarization with negative-sequence current (I2) or zero-sequence current (I0) is not reliable during the open-pole interval. The open pole makes the power system unbalanced, causing negative- and zero-sequence currents to flow. The consequence to distance elements polarized with sequence component currents, as in (3) and (8), is that the polarization becomes unreliable. Depending on the load flow direction, I2 and I0 will have different directions. Fortunately, there are other distance elements that will reliably operate during an open-pole condition [14]. The positive-sequence voltagepolarized mho element is stable during open-pole intervals and will reliably detect power system faults during this condition. In a practical scheme, the phase and ground quadrilateral elements should be disabled when an open-pole condition is detected. The high-speed quadrilateral distance element is implemented with incremental quantities and does not need to be disabled during the open-pole interval. IV. SETTING THE QUADRILATERAL DISTANCE ELEMENT Consider the A-phase-to-ground fault circuit of Fig. 4. Equation (20) determines the apparent impedance (Zapp) that the relay installed at the left side of the line measures as a function of fault voltages and currents. Equation (21) determines Zapp as a function of Rf and fault location m. VA Zapp = IA + k0 • IR (20) Zapp = m • ZL1 + KR • Rf (21) In (21), KR is a factor that depends upon the positive- and zero-sequence current distribution factors (C1 and C0) and is equal to: KR 3 = (22) 2 • C1 + C0(1 + 3• k0) C1 and C0 are equal to: (1 − m) • ZL1 + ZR1 C1 = (23) ZS1 + ZL1 + ZR1 (1 − m) • ZL0 + ZR0 C0 = (24) ZS0 + ZL0 + ZR0 k0 is the zero-sequence compensation factor equal to: ZL0 − ZL1 k0 = (25) 3• ZL1 For no-load conditions (δ equal to 0) and homogeneous systems, the resistive blinder of the adaptive quadrilateral element will assert for an Rf that satisfies this condition: Rapp < Rset (26) Rapp = Real(KR) • Rf (27) where Rset is the resistive reach setting. Alternatively, we can calculate Rapp using relay voltage and currents for a fault at m according to (28). Rapp = Real( Zapp) − m • Real( ZL1) (28) Adaptive Phase and Ground Quadrilateral Distance Elements | 75
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$12.00 Journal of Reliable Power Vo
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Journal of Reliable Power Volume 1
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Capable of running protection calcu
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Both P and Q are two-input phase an
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TABLE 1: MHO ELEMENT POLARIZING CHO
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For an Aφ-ground fault on the syst
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The most onerous 3φ fault is one w
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If the angle is near +120°, then t
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Impedance-Based Fault Location Expe
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A. Simple Reactance Method From Fig
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Figure 9 shows a screen capture of
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The relay then performs “torque
Page 25 and 26: IX. LAB TEST SETUP Several line fau
Page 27 and 28: APPENDIX The following are the rela
Page 29 and 30: The following shows the analog math
Page 31 and 32: Digital Communications for Power Sy
Page 33 and 34: increasing security by a factor of
Page 35 and 36: The receiver amplifier is the major
Page 37 and 38: Noise from faults or other sources
Page 39 and 40: 80 60 40 20 R F 100 3 3 S 2 5 6 4 1
Page 41 and 42: 15. A POTT scheme implemented over
Page 43 and 44: Transmission Line Protection System
Page 45 and 46: One-Cycle Directional Element Figur
Page 47 and 48: element misoperation. Shunt reactor
Page 49 and 50: • SW2 is in Position 1 when there
Page 51 and 52: Complete reclosing relay supervisio
Page 53 and 54: IX. BIOGRAPHIES Armando Guzmán, P.
Page 55 and 56: 2 II. COMMON ZONE TIMING In June 20
Page 57 and 58: 4 ment 67N2 after a 1-cycle carrier
Page 59 and 60: 6 VI. ZONE 1 OVERREACH DUE TO CVT I
Page 61 and 62: 8 1_VA 1_VB 1_VC 2_VA 2_VB 2_VC 3_V
Page 63 and 64: 10 The phasors during the fault are
Page 65 and 66: 12 The prefault data from the backu
Page 67 and 68: 1 Adaptive Phase and Ground Quadril
Page 69 and 70: 3 C. Short Line Applications A shor
Page 71 and 72: 5 II. QUADRILATERAL DISTANCE ELEMEN
Page 73 and 74: 7 For the purpose of implementing t
Page 75: 9 The three-phase fault detection e
Page 79 and 80: 13 Fig. 24 shows the apparent resis
Page 81 and 82: 15 B. Adaptive Resistance Element F
Page 83 and 84: 17 Fig. 34 and Fig. 35 illustrate t
Page 85 and 86: Line Protection Bibliography Issue
Page 87 and 88: Hou, Daqing, and Jeff Roberts. “C
Page 90: ©2010 Schweitzer Engineering Labor
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